The present invention relates to a new and improved construction of a dressing apparatus for a substantially plate-shaped or dished grinding wheel of a tooth flank-grinding machine.
Generally speaking, the dressing apparatus of the present development is of the type comprising a dressing carriage or slide which can be radially advanced or fed by means of a radial drive in relation to the grinding wheel. The dressing carriage carries a dressing tool for dressing the outer surface of the grinding wheel and a feeler for scanning the working end surface or active rim of the grinding wheel and for controlling its axial advance or infeed movement, the feeler always moving radially with respect to the grinding wheel during the advancing or infeed movement.
According to a prior art dressing apparatus of this species, for instance as disclosed in the German Pat. No. 2,644,890 and the corresponding U.S. Pat. No. 4,143,637, the dressing tool is constituted by a rotating dressing disk which is effective at its end face, this rotating dressing disk or wheel being mounted at the dressing carriage in such a manner that its axis of rotation extends radially with respect to the grinding wheel and coincides with the direction in which the dressing carriage is advancable by the radial drive. The feeler for controlling the axial advance motion of the grinding wheel, and which has not been illustrated in the aforementioned German Pat. No. 2,644,890, is attached at the dressing carriage such that it scans the end surface of the grinding wheel directly radially within the working location of the dressing tool. This arrangement has been found to be satisfactory for grinding methods, such as the 0.sup.o -grinding method (discussed for instance in applicant's handbook, entitled "MAAG-Taschenbuch (MAAG-Gear Book), Zurich, 1963, pages 259 et seq), wherein two mutually parallelly arranged grinding wheels simultaneously engage at a respective tooth flank, and thus, only work with a small outer marginal region of their free end surface. If it is intended to realize with such grinding techniques high dimensional accuracy and surface quality, then the active end surface of the grinding wheel or each grinding wheel, as the case may be, must be checked at brief time intervals by a feeler and, depending upon the response of a control device, must be axially repositioned and possibly dressed, and furthermore, the outer surface of the grinding wheel must be machined at certain time intervals, so that it forms, together with the end surface, a sharp edge or rim and always remains at just that width which avoids any crumbling of the grinding wheel at its outer rim or edge.
There have also become known to the art grinding techniques wherein a sharp-edged grinding wheel rim is not an absolute requirement and is not even desirable in consideration of economical utilization of the grinding wheel. Even so, with such grinding techniques it is necessary to dress the grinding wheel or each grinding wheel at certain time intervals at their end surface and, usually over larger time intervals, also at their rounded outer surface. There is preferably used for the dressing of the outer surface a dressing tool in the form of a roll, the axis of rotation of which is arranged parallel to that of the grinding wheel and whose outer surface profile is complementary to that of the grinding wheel. When using such dressing tool or others which are suitable for dressing a rounded rim or edge of the grinding wheel, it is difficult to secure the feeler serving to control the axial advance movements of the grinding wheel in such a manner at the dressing carriage that it directly scans the narrow ring-shaped end surface of the grinding wheel directly radially within the dressing tool which dresses the grinding wheel-rim or edge. It would be conceivable to arrange this feeler upon a separate feeler carriage which is independent of the dressing carriage. This feeler carriage then could be advanced in synchronism with the dressing carriage at a predetermined angle with respect thereto and radially in relation to the grinding wheel. Yet, this arrangement would require considerable equipment expenditure, firstly, because the movements of the dressing tool and the feeler must be coordinated extremely accurately with respect to one another, so that the grinding wheel always has the required shape and position in relation to the tooth flank which is to be ground, and accordingly, is able to produce the requisite working accuracy